Infrared surface heating unit



1967 D. c. SIEGLA INFRARED SURFACE HEATING UNIT v 5 Sheets-Sheet 1 Filed Feb. 1, 1965 0 Donald C. Sieg/a BY v INVENTOR.

H/ls Afro/n e y Oct. 3, 1967 D. c. SEGLA 3,345,498

INFRARED SURFACE HEATING UNIT Filed Feb. 1. 1965 3 Sheets-Sheet 2 INVEN TOR. Donald 6. Sieg/a His Attorney 1957 D. c. SIEGLA INFRARED SURFACE HEATING UNIT 3 Sheets-Sheet 5 Filed Feb. 1. 1965 INVENTOR. Don 0/0 6. Sky/a His Attorney & K

United States Patent 3 345,498 INFRARED SURFACE HEATING UNIT Donald C. Siegla, Dayton, Ohio, assignor to General Motors Corporation, Detroit, Mich., a corporation of Dela- Ware Filed Feb. 1, 1965, Ser. No. 429,305 1 Claim. (Cl. 219-464) ABSTRACT OF THE DISCLOSURE This invention relates to surface heating units and more particularly to surface heating units of the infrared type.

Present-day surface heating units are characterized, in the case of electrical units, by direct conductive heating of associated utensils. Such units typically include a utensil supporting spirally-wound sheathed tubular electrical resistance heating element or the like that has a substantial thermal lag before utensil heating occurs. Moreover, uneven contact between such surface heating units and utensils supported thereon can materially reduce the conductive heat transfer to the utensil. In order to reduce such thermal lag and to improve heat transfer to utensils, infrared surface heating units have been developed wherein a tungsten resistance element is utilized in association with a parabolic reflector to produce a unit having low thermal lag and good utensil heating characteristics. A representative unit of this type is disclosed in Patent No. 2,859,368, issued Nov. 4, 1958. While these units are suitable for their intended purpose, they are necessarily, because of the parabolic reflector therein, relatively large, especially in a vertical direction and, thus, require substantial modifications in present-day ranges for use therein. Because of their relatively large size, they require a reduction in size of oven or storage compartments within an associated domestic range appliance. Furthermore, such units are relatively expensive as compared to presently used sheathed electrical resistance heating elements.

An object of the present invention, therefore, is to improve surface heating units for association with domestic electric ranges and the like while retaining the dimensional configurations of presently used spirally-wound sheathed resistance heating elements by the provision of a low-profile envelope surrounding a high-temperature infrared radiant energy emissive resistance element out of direct heat conductive relationship with the envelope and wherein the resistance element is arranged throughout substantially the full planar extent of the surface unit in spaced relationship below an infrared transmissive upper utensil supporting planar surface portion of the envelope.

Yet another object of the present invention is to im prove infrared surface heating units by the provision of a low-profile outer envelope including an upper plate of infrared transmissive material for supporting a utensil, a lower plate of low-thermal mass and an infrared emissive resistance element supportingly received within the envelope by means for locating the element out of direct conductive heat transfer relationship with the surrounding envelope.

A further object of the present invention is to adapt direct infrared heating to surface heating units for use on domestic ranges by the provision of a pancake-like enclosure surrounding an infrared emissive resistance heating element in spaced relationship thereto and wherein the enclosure includes means for directing substantially all of the infrared radiation from the resistance element against a supported utensil for raising its temperature.

Yet another object of the present invention is to im prove infrared surface heating elements by the provision of an infrared emissive resistance element disposed throughout substantially all of the planar extent of the surface unit out of direct heat transfer relationship with an upper infrared transmissive utensil supporting plate and supported in spaced relationship with respect to a lower supporting plane located in close spaced parallelism with the upper plate having an infrared reflective upper surface thereon whereby substantially all of the radiant energy of the resistance element is utilized for heating a supported utensil by direct infrared radiation heating.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein preferred embodiments of the present invention are clearly shown.

In the drawings:

FIGURE 1 is a view in perspective of a domestic range including surface heating units of the present invention;

FIGURE 2 is an enlarged view in vertical section taken along the line 2-2 of FIGURE 1;

FIGURE 3 is an enlarged sectional view of the resistance element in the surface heating unit of FIGURE 2;

FIGURE 4 is an enlarged view in top elevation, partially broken away, of the surface heating unit shown in FIGURE 1;

FIGURE 5 is a view in top away, of another embodiment and FIGURE 6 is a view in vertical section taken along the line 6-6 of FIGURE 5.

Referring now to the drawings, in FIGURE 1, a domestic electric range 10 is shown having a plurality of surface heating units 12 thereon selectively energizable by suitable temperature controllers 14 representatively shown as being disposed on a rearwardly located control panel 16 of the range 10.

In FIGURES 2 and 4, each of the units 12 are more particularly shown as being disposed within openings 18 defined by a supporting ring 20 formed in the sheet metal upper surface of the range 10. The supporting ring 20 includes an upwardly curved top portion 22 surrounding the unit 12 and a downwardly turned portion 24 having a radially inwardly turned edge 26 for forming a continuous surface for supporting the heating unit 12 within the opening 18.

On the ring-like supporting surface formed by edge 26 a resilient annular member 28 of a suitable heat resistant material such as silicone rubber is disposed for supportingly receiving a lower plate 30 of the unit 12 along a continuous peripheral portion 32 thereof to absorb impact loadings between the unit 12 and its supporting structure. In the embodiment of the invention shown in FIGURES 2 and 4, the lower plate 30 is formed of a suitable electrically insulating ceramic material such as alumina, steatite or the like having a relatively low-thermal mass.

The lower plate 30 has an upper planar surface 34 thereon coated with a layer 36 of a suitable infrared reflective material such as gold, silver or the like. At spaced points on the upper surface 34 a plurality of button-like resistance element supporting posts 38 are disposed being formed in this embodiment of the invention as integral elevation, partially broken of the present invention;

a) upwardly directed extensions of the lower plate 30. Each of the buttons 38 has a groove 40 formed therethrough for supportingly receiving a portion of a continuous spiral formed infrared emissive electrical resistance element 42 which extends across substantially the full planar extent of the unit 12.

The support buttons 38 are grouped along radial lines on the support plate 30 at spaced circumferential points therealong whereby the spiral ribbon 42 is supported throughout its length out of direct heat transfer contact with the upper reflective surface 34 of the support plate 30.

The spirally-wound resistance element 42 is connected at the innermost end thereof to a terminal 44 directed through a center post 46 of the lower plate 30* outwardly thereof and at its outermost end to a terminal 48 directed through a post 50 outwardly of the lower plate 30 whereby a suitable power source can be connected to the resistance element 42 for maintaining it at a desirable operating condition under the control of the controllers 14.

In accordance with certain of the principles of the present invention, the resistance element 42 has a maximum practical ratio of cross-sectional area to infrared radiating outer surface area, for example, a ribbon-like, cross-sectional configuration, best seen in FIGURE 3 as including a major axis 52 of substantially greater dimension than a minor axis 54 therethrough. By virtue of this construction, the ribbon 42 between the supported points thereon has a substantial vertical structural strength whereby, when the resistance element is energized, it will resist any substantial tendency to sag between its support points so as to cause any portion thereon to electrically contact another portion thereon so as to short out the unit. The large radiating surface also reduces the length of the resistance element required for a given infrared output and thus obviates problems of maintaining adjacent portions of the coil out of electrical contact with one another. Furthermore, by the provision of a substantial groove 40 in each of the support buttons 38, upon energization of the resistance element 42, expansion thereof caused by self-heating is adequately compensated and likewise, upon contraction following deenergization of the resistance element 42, the coil pattern is free to contract into the position illustrated in FIGURES 2 and 3. While a ribbon-like resistance element with large surface area to thermal mass and good strength has been shown, the invention also contemplates the use of like sectional configurations, for example, diamond shapes, twin-sectioned angle shapes, tubular cross-sectional shapes and the like.

In accordance with other principles of the present invention, the resistance coil 42 is constructed of a hightemperature electrical resistance material from a nickelchromium family or an iron chromium aluminum family or the like having desirable strength and electrical characteristics when the resistance element is self-heated into the range of 1500 F. to 2000 F.

To protect the resistance element 42 an upper utensil supporting plate 56 is located thereabove and includes a downwardly depending continuous inner peripheral edge portion 58 that is supportingly received by the peripheral portion 32 of the support base 30 so as to locate the upper plate 56 in spaced relationship with respect to the electrical resistance element 42. By virtue of this arrangement, when the coil 42 is energized, emitted infrared energy therefrom either directly passes through the upper plate 56 into radiant transfer relationship with the utensil supported thereon or is reflected from the upper surface of the lower plate 30 into direct radiant heat transfer relationship with the supported utensil. The upper plate 56 is a high-strength infrared transmissive member constructed from quartz, a high silica glass such as Vycor made by Corning Glass Works, or a recrystallized glass ceramic such as Cer-Vit manufactured by Owens-Illinois Glass Company. These materials are merely representative and in each case are selected so that they transmit substantially all of the infrared energy from a particular resistance element to an article supported upon the top plate 56. The plates 30, 56 have a low-profile much like that of sheathed resistance type surface heating units and they also serve as a surrounding protective envelope for the resistance element 42.

One important aspect of the invention is the fact that the spirally-wound resistance coil 42 is maintained in spaced relationship to both the low-thermal mass lower plate 30 and the upper utensil supporting plate 56. The resistance coil 42 is thereby quickly responsive to a predetermined power source connected thereacross to self-heat to a predetermined elevated temperature for effective infrared emission without any substantial conductive cooling effect occurring between it and the rest of the surface heating unit 12. Accordingly, the unit is characterized by a very low thermal lag as compared to sheathed resistance type surface heating units. It thus has a very short warm-up period before it begins to effectively increase the temperature of the utensil on the support plate 56.

By virtue of the above-described structure an unusually effective infrared radiation heattransfer occurs between the resistance element 42 and the utensil to be heated. The net energy interchange therebetween can be expressed by the equation:

where Q=net heat transfer (B.t.u./hr.)

More specifically, by thermally isolating theresistance element 42 from the other parts of the unit, it will operate, for example, in the range of 1500 F.-2000 F. as compared to a'sheathed resistance element which operates in the range of 500 F. when a vessel is supported in direct heat-conductive relationship therewith. Thus, T in the above formula increased to the fourth power causes a materially improved heat transfer Q in the case of the present invention. Furthermore, by the provision of a reflective surface. 34 on the lower plate 30 infrared emission from element 42 which does not directly radiate against the utensil will by reflection be directed thereagainst. Thus, substantially all of the infrared emission from element 42 is used to radiantly heat the supported utensil. The radiating surfaceA of the element 42 also is selected to be relatively large for a particular element cross-sectional area.

Another feature of the embodiment shown in FIGURES 1 and 3 is the provision of a radially outwardly directed peripheral lip 60 formed continuously around the unit 12 in spaced relationship to the upwardly curved part 22 of the support ring 20 to form a passageway 62 therebetween. The lip 60 serves to prevent spillage from supported utensils from flowing interiorly of the envelope formed by the upper and lower plates 56, 30 to adversely affect the operation of the resistance element 42. Any spillage that does pass through the passageway 62 between the lip 60 and the ring 20 flows beneath the surface cooking unit 12 through weep openings 64 formed in the resilient shock absorbing member 28.

In the embodiment of the invention shown in FIG- URES 5 and 6 a surface heating unit 70 is shown supported within an opening formed by a support ring 72 like 20 of the first embodiment. In this arrangement an annular resilient shock absorbing member 74 on the ring.

72 supportingly receives a thermal insulating ring 76 of a suitable material such as asbestos. The ring 76, in turn, supportingly receives a lower support plate 78 of the unit 70 formed of sheet metal to have a supported peripheral portion 80 thereon resting on the ring 76 and an upwardly turned edge 82 which supportingly receives a depending continuous inner peripheral portion 84 of an upper utensil supporting plate 86 formed of a suitable infrared transmissive material as discussed in the first embodiment.

In this embodiment of the invention the lower support plate 78 is of aluminum and has an upper planar surface 88 thereof polished to serve as an infrared reflective surface. The reflective aluminum surface 88 has a suitable infrared transmissive protective coating 90 such as silicon monoxide thereon to prevent oxidation of the surface 88. A plurality of electrical insulating buttons or posts 92 each has a small diameter portion 94 thereon directed through the lower plate 88 in supported relationship therewith and includes an upper large diameter end with a groove 96 therethrough for supportingly receiving a spirally-wound, continuous resistance heating element 98 like that in the first embodiment. The support buttons 92 are arranged like those in the first embodiment serving the same purpose herein as in the first embodiment.

Like in the first embodiment, the spirally-wound resistance element 98 is connected at the innermost end thereof to a terminal 100 directed through a post 102 exteriorly of the unit 70 and at the opposite end thereof to a terminal 104 and likewise directed through a post 106 exteriorly of the unit. As was the case in the first embodiment, the resistance element 98 is selectively energizable under the control of a suitable switch to operate in a predetermined temperature range wherein a substantial amount of infrared energy is emitted therefrom for heating utensils supported on the upper plate 86.

The buttons 92 support the resistance element 98 out of direct heat transfer relationship with the upper plate 86 and the lower plate 78 whereby there is little conductive heat transfer from the resistance element 98 to the remainder of the surface heating unit 70 so that energy input thereto will quickly increase the temperature thereof Without any substantial thermal lag to eifectively immediately heat a supported utensil on the unit 70 by infrared radiation.

Like in the first embodiment, the resistance heating element 98 has a relatively low thermal mass and is of a cross section as shown in FIGURE 3 for the reasons previously stated.

In this embodiment of the invention the upper plate 86 further includes a peripheral flange 108 thereon forming an overhanging lip to direct spillage away from the unit 70. Any spillage directed between the upper plate 86 and the support ring 72 flows beneath the unit 70 through weep openings 110 in the shock absorbing ring 74.

In view of the aforesaid descriptions of the various embodiments of the invention, it will be appreciated by those skilled in the art that the infrared surface heating unit of the present invention is characterized by an unusually low thermal lag prior to effective radiant energy heating and, furthermore, constitutes a low-profile or pancake-like configuration that is unusually well suited for use in present-day ranges without any substantial modification thereof. Furthermore, the infrared surface units of the present invention are constructed and arranged so that the resistance heating element thereof is able to be operated either continuously or pulsatingly over long pe- 6 riods of time with a high degree of reliability. Furthermore, the units can be quickly removed for cleaning and are constructed and arranged to prevent cooking spillage from adversely affecting their operation.

While the embodiments of the present invention as herein disclosed constitute preferred forms, it is to be understood that other forms might be adopted.

What is claimed is as follows:

In an infrared surface heating unit, the combination of an upper utensil supporting plate of infrared transmissive material, a lower reflector plate, coacting means on said upper plate and reflector plate for forming an open space therebetween, an infrared emissive resistance element located within said space having a ribbon shaped cross-section with a major axis and a minor axis, an input terminal carried on said reflector plate, an output terminal carried on said reflector plate, said resistance element having one end thereof electrically connected to the input terminal and an opposite end thereof electrically connected to said output terminal, said ribbon shaped element extending in a spiral form between said input and output terminals throughout substantially the full planar extent of said upper utensil supporting plate, a plurality of posts supported on said reflector plate at spaced apart locations thereon each including an upper end portion thereof located in spaced relationship below said upper utensil supporting plate and ,above the upper surface of said reflector plate, each of said posts including a vertically directed slot therein extending across the upper end of said post, said ribbon shaped resistance element having a segment thereof extending through each of said vertically arranged support post slots and having the major axis thereof directed vertically of said slots, said slots having a sufiicient width to allow for radial movement of said resistance element upon energization thereof to compensate for heat generated expansion of said spiralled resistance element, said resistance element having only the lower edge thereof in heat transfer contact with said support posts and having the remainder of the planar extent thereof out of direct contact with both said upper utensil supporting plate and said reflector plate whereby upon said input and said output terminal being connected across a power source the electrical energy flows through said resistance element which produces self-heating of said resistance element into a visual light emitting range observable through said upper utensil supporting plate to indicate operation of the unit, said support posts being constructed of heat insulating material to prevent heat transfer from said resistance element to said reflector plate.

References Cited UNITED STATES PATENTS 1,102,249 7/1914 Denhard 219520 1,468,385 9/1923 Lamb 2l9467 X 1,905,770 4/1933 Walker et a1 219-467 X 2,179,934 11/1939 Jones 219-538 2,490,602 12/1949 Schick 219467 X 2,570,975 10/1951 Osterheld 219468 X 2,770,704 11/1956 Razlag 219-345 2,799,765 7/1957 Jenkins et a1. 219-464 X 2,870,316 l/l959 Ferguson 219-464 X RICHARD M. WOOD, Primary Examiner.

L. H. BENDER, Assistant Examiner. 

